Graphene, atomically thin carbon sheets, and its structural derivatives (bi- or few-layered graphene) have attracted great attention due to their exceptional charge transport, thermal, optical and mechanical properties. Graphene materials have been evaluated for applications in electronics, energy conversion and storage technologies, gas sensing technology, and in many other fields.
As a single sheet, graphene was first isolated by micro-mechanical cleaving of graphite by an adhesive substrate. Another method to produce graphene is epitaxial growth on a copper or nickel substrate from a diluted hydrocarbon atmosphere at ˜1300 K. After a chemical etching of the metal substrate, the graphene layers can be detached and transferred to another substrate. An approach to producing few-layered graphene is ultrahigh vacuum annealing of a silicon carbide (SiC) wafer. This method requires no transfer before use in processing devices, which makes it attractive for the semiconductor industry.
The reaction between halogens (e.g., chlorine) and refractory carbides (e.g., SiC, TiC, WC, Ti3SiC2) at temperatures of 900-1500 K are also known to produce various carbon materials. In this process, the chlorine selectively etches the metal (Ti, W) or metalloid (Si) from the carbide lattice resulting in disordered porous carbons, which are often referred to as carbide-derived carbons (CDCs). Chlorination of some carbides results in CDC particles with surface graphene layers.
Oxidative exfoliation of graphite and subsequent chemical reduction is one of the most efficient methods for low-cost production of graphene. However, the chemical reduction cannot remove many irreversible lattice defects introduced by the oxidation process. These defects degrade the electronic properties of graphene. Nano-sheets obtained by this chemical modification strategy also suffer from relatively low surface area and readily form aggregated structures, which greatly impact their application performance. Therefore, it is important to search for new effective approaches for synthesis of graphene nano-sheets with desired properties.
Recently, several attempts have been made to produce a variety of advanced carbon-based nano-structures, including graphene, by self-sustaining combustion reactions. For example, porous disordered carbon “onions” were produced by exothermic reaction between sodium azide (NaN3) and in hexachlorobenzene (C6Cl6) or hexachloroethane (C2Cl6). A different approach based on self-sustained direct reduction of CO2 and CO gases by metals (Li, Mg, Ca, B, Ti, Zr, and Al) is also proposed to produce layered graphite materials. Researchers have suggested that the Mg reduction of CO2 is the most optimal system to produce few-layered graphene. It has also been demonstrated that short-term local heating of a graphene oxide (GO) sample may initiate a self-propagating deoxygenation reaction resulting in reduced-GO.
However, each of the methods currently used for preparing carbon-based nano-structures are limited in terms of scalability or their resulting purity. Accordingly, new methods of synthesizing carbon-based nano-structures are needed to advance the fields of electronics, energy conversion and storage technologies, gas sensing technology, and coatings. Preferably the methods would be cost-effective relative to current technologies and scalable for kilogram syntheses of carbon-based nano-structures such as graphene.